Investigations are designed to learn more about the cellular control and transport of mineral ions which become incorporated into developing enamel and defensive mineralization of primary dentin. Maturative ameloblasts of fluorotic rats contain intracellular deposits of crystalline mineral. Injected cobalt causes a temporary reduction or cessation of mineral ion transport into a forming enamel front. These experimental models are used to trace the pathway of mineral ions as they pass from tissue fluids to mineralizing enamel utilizing electron microscopy, histochemistry and electron microscopic autoradiography. Defensive mineralization of rat molar primary dentin is being further analyzed. The enamel-free region of dentin is being examined microradiographically and electron microscopically before and after eruption of the tooth to ascertain the rate and pattern of intratubular mineralization. Microradiography, scanning and transmission electron microscopy are being used to investigate sclerotic and secondary human dentin. The claimed protective value of these tissues needs to be assessed, and details of their physiologic and induced patterns of formation elucidated. BIBLIOGRAPHIC REFERENCES: Walton, R.E. and Eisenmann, D. R. 1975. Ultrastructural examination of dentine formation in rat incisors following multiple fluoride injections. Arch Oral Biol, 20:485-488. Neiman, A. and Eisenmann, D. R. 1975. The effect of strontium, cobalt and fluoride on rat incisor enamel formation. Anat Rec, 183: 303-322.